1. Field of the Invention
The present invention relates in general to the tracking of public transit vehicles, and more particularly to inferring, from devices transiently present on those vehicles, both the location of those vehicles and any deviation from previously published schedules, and the automated provisioning of this information to interested end users.
2. Description of Related Art
A significant impediment to the use of public transit remains the possibility of vehicles arriving later or earlier than their scheduled times. A commuter may be aggravated by arriving late at a destination, missing a train or bus, or simply by investing time waiting for a late vehicle. The latter kind of waiting both reduces the time until the vehicle arrives, and increases the likelihood of failing to reach the destination on time. As time passes, this cost-benefit conflict becomes more acute, resulting in ever-increasing anxiety. So common is this last type of irritation that psychologists have given it a name: “The Rosencrantz and Guildenstern effect” (named after the following passage in the play Rosencrantz and Guildenstern are Dead by Tom Stoppard: “We've traveled too far, and our momentum has taken over; we move idly towards eternity, without possibility of reprieve or hope of explanation.”)
FIG. 1 illustrates example situations in which public transit vehicles deviate from their scheduled routes, possibly causing aggravation for commuters. Four trips are shown, with distance traveled on the horizontal axis and time increasing down the vertical axis. Published schedules are shown by dashed lines, while the actual position of each vehicle is shown by a solid line.
Trip #1 departs on time but moves slowly between stops #1 and #2, arriving a few minutes late at stop #2. It loads and unloads passengers in the allotted amounts of time at each stop, but remains a few minutes behind schedule all the way to stop #4.
Trip #2 also departs on time and moves slowly between stops #1 and #2. It spends a long time unloading and loading passengers at stop #2. However, it moves quickly, arriving at stop #3 at its scheduled departure time, and catching up to schedule by stop #4.
Trip #3 beats its schedule to stop #2 and waits until its scheduled departure time until continuing. It then arrives at stop #3 behind schedule, but unloads and loads passengers quickly and proceeds to stop #4 exactly on schedule.
Trip #4 leaves stop #1 behind schedule and is on track to arrive late at stop #2.
Current technologies that address the problem of public transit vehicles arriving before or after scheduled times use Automatic Vehicle Locating (AVL) systems. The implementation of these systems involves significant infrastructure development on the part of the agency that operates the vehicles. Typically, permanent transceivers are installed in each vehicle that must be tracked, and the locations of the vehicles are determined using Global Positioning System (GPS) satellites. This position information is transmitted back to a central facility using a satellite, terrestrial radio or cellular connection from the vehicle to a radio receiver, satellite or nearby cell tower. After capture, the location data of vehicles is processed and made available to end users via signage, phone recordings, or Internet sites. One example of such a system is disclosed in U.S. Pat. No. 6,006,159 to Schmier et al., which teaches a system for notifying passengers waiting for public transit vehicles of the status of the vehicles using a GPS device installed in each vehicle. A similar system is disclosed in U.S. Patent Application Publication 2006/0217885 to Crady et al., which teaches end users querying a vehicle position aggregation system that receives data from GPS devices installed in vehicles belonging to different vehicle fleets.
These existing solutions to the problem of tracking public transit vehicles are extremely capital-intensive for fleet operators. Transit agencies, which are notoriously underfinanced, must equip every vehicle with a robust, permanent GPS receiver, processor, and a transmitter to relay their position to the central tracking system, and maintain and upgrade these devices. Transit agencies must also internalize the costs of buying or leasing large, central data aggregation systems. Further, ongoing operation requires the payment of data transmission fees, either to lease wireless frequencies directly or to sublease them from another operator.
Many transit agencies make Internet-based route and schedule publications and databases available to the public on the Internet. The most advanced sites include web pages that are capable of planning an entire door-to-door trip, including transfers between vehicles. Several of these transit agencies have standardized their published data formats so that they may be used by other utilities, such as the Google Transit™ trip planning service provided by Google Inc. of Mountain View, Calif.
Further, there are a proliferation of consumer devices, typically mobile cellular phones with advanced capabilities, that are both aware of their own locations using maps of urban wireless service environments, and capable of transmitting information to distant servers wirelessly. At present, there are millions of these small devices that have sufficient capabilities to perform a transit agency's vehicle tracking needs without requiring the agency to incur any expense. At any given moment, thousands of these devices are already transiently present on public transit vehicles and operating without any investment from the operating transit agencies.